flavonolignans

Flavonolignans are a class of plant secondary metabolites formed by the oxidative coupling of a flavonoid unit, typically taxifolin, with a lignan unit derived from coniferyl alcohol. This coupling yields a group of polyphenolic compounds most notably present in milk thistle seeds (Silybum marianum). The best-known members of the family are the components of the silymarin complex: silibinin (silybin A and B), silychristin, silydianin, and the diastereomers isosilybin A and B.

Biosynthesis is thought to proceed in seeds through oxidative coupling reactions, often involving peroxidase-type enzymes, that link taxifolin with a lignan precursor to form the flavonolignan skeleton. The resulting compounds are relatively lipophilic and are typically extracted with organic solvents.

Properties and applications: Flavonolignans exhibit antioxidant activity and have been studied for hepatoprotective effects. Silymarin is used as a dietary supplement claiming liver-protective benefits; however, bioavailability is limited and clinical evidence for disease-modifying therapy remains inconclusive. Proposed mechanisms include free radical scavenging, stabilization of hepatocyte membranes, and modulation of inflammatory signaling.

Occurrence beyond milk thistle: while milk thistle is the primary source, related flavonolignans have been reported in trace amounts in other plants, but the association is weaker there.

Safety and regulation: Silymarin is generally well tolerated; adverse effects are usually mild, including gastrointestinal symptoms or allergic reactions. It can interact with certain medications by affecting hepatic enzymes, so medical supervision is advised during concurrent use.